Our recent studies have indicated that there are two types of cardic myosin, each with a distinctive pattern in regard to stability, response to sulfhydryl reagents, activation energy and adenosinetriphosphatase activity, and the level of thyroid hormone appears to determine which type of myosin is synthesized. We will attempt to characterize the 2 types of cardiac myosin further, to study human cardiac myosin and deterine whether thyroid hormone affects the myosin of other tissues. The control of cell multicplication in the arterial wall will be studied in regard to the stimulatory effectiveness of growth hormone and serum growth factors and in regard to inhibitory substances, both natural and pharmacological. The influence of hypertrophy on cardiac muscle contractility will be studied further, particularly in regard to the "pure" hypertrophy in rats transplanted with MtT-F4 tumors. The effect of human growth hormone and other human pituitary factors on serum lipids will also be further explored. A separate "diabetogenic" factor will be sought in the various pituitary fractions obtained in the course of purification of human growth hormone. The physicochemical and biological characteristics of angiotensin-converting enzyme will be further investigated.